Permanent Magnets are widely used in the motor of vacuum cleaner, with a stable magnetic field and when electrified then produce electromagnetic field to drive the motor rotate.

When the changing electric currentgoes through acoustics, magnet become electromagnet, current direction changes a, electromagnet keeps moving back and forth due to "electrify conductor is in the force movement in magnetic field" in the meanwhile drives paper basin to vibrate back and forth as well, then acoustics make a sound.

Electromagnetic relays are automatic switches controlled by electromagnets. Using electromagnetic relays can choose low voltage and low current to control high voltage and strong current, to achieve remote operation.